The invention relates to power semiconductor modules.
Conventional power semiconductor modules include one or more power semiconductor chips which are arranged on a plane ceramic substrate which includes a metallization on at least one side. At least one of such ceramic substrates is soldered to a metallic base plate of the module. To improve cooling, the base plate may be pressed against a heat sink.
The metallized ceramic substrates are pressed against the heat sink without a metallic base plate in between. To reduce the heat transmission resistance between the substrate and the heat sink, a layer of heat conductive paste is required. As the thermal conductivity of such a heat conductive paste is limited, the thickness of the layer of heat conductive paste needs to be very thin. However, apart from the locations to which downforce is applied to the substrates, the substrates tend to bend upwards, i.e. away from the heat sink. The result is a non-uniform thickness of the heat conductive paste.
To avoid this, the downforce is sought to be uniformly distributed over the substrate. For this, mechanical structures are provided to apply pressure onto the substrate all over the substrate area. However, due to the presence of semiconductor chips, bonding wires etc., the options to apply pressure all over the substrate area are limited.
For these and other reasons, there is a need for the present invention.